Drinking alcohol on a regular basis before a first pregnancy can set the stage for breast cancer later in life. A study found an 11 percent increased risk of breast cancer among women who drank 10 grams (about one-third of an ounce) of alcohol six times a week compared to women who didn’t drink any alcohol.

More than 91,000 women participated in the study and were followed for 20 years to determine how drinking (or not drinking) affected their breast cancer risk. None had a history of cancer to start with. The study also linked pre-pregnancy drinking with an increased risk for proliferative benign breast disease, itself a breast cancer risk.

The researchers reported that 1,609 women developed breast cancer and 970 developed proliferative benign breast disease over the 20 years. They noted that breast tissue in women who have not been pregnant is particularly susceptible to carcinogens, which they suggested might help explain the breast cancer threat posed by drinking before pregnancy. They also wrote that the increased risk tended to be “more pronounced” among women with a longer time interval between the onset of menstruation and first pregnancy compared with women with a shorter interval.